The invention concerns an axial flow rotary separator for a crop harvester in which a rotor rotates within an elongated, surrounding casing and more particularly, one in which finger-like elements of the rotor intermittently engage a mat of crop material while propelling it in a generally spiral path within the casing.
For convenience, crop material engaging elements arranged to penetrate and engage a crop material flow only intermittently will often be referred to below as "fingers" or "finger-like elements" although, of course, the elements may take many forms while still functioning in essentially the same way.
In the discussion which follows, the vehicle for the axial flow rotary separator is assumed to be a self-propelled combine harvester as used for harvesting a variety of grain and other crops. However, separators of this type may of course be used in pull-type combine harvesters as well as in stationary threshing and separating operations.
Although the long history of mechanical threshing and separating of agricultural grain crops has been dominated by the conventional arrangement of transverse threshing cylinder upstream of a rack or straw walkers, there have also been attempts spanning many years to develop axial flow rotary separation. In recent years, combine harvesters embodying this principal have captured a significant portion of the market. Typically their rotors include an upstream threshing portion coaxial with a downstream separator portion. The separating operation per se is carried out on threshed crop material to separate the remaining grain from straw and leaves etc. However, in keeping with common usage, the term separator will sometimes be used in this application to describe a combination of components including infeed arrangements for a rotor or rotors, and discharge provisions in combination with an actual separator portion (and an upstream threshing portion if it forms part of the axial flow unit).
Conventional axial flow rotary separators with driven rotors depend for axial indexing on sliding motion between crop material and angled surfaces within the separator, such as angled blades on the rotor or helical guide vanes on the casing or a combination of the two. Crop engaging elements of the rotor are carried in fixed relation to the rotor frame and propulsion of crop material is not positive. Crop material is deflected axially by angled blades or guide vanes but, typically, there is a strong tendency for material to ride over the rotor elements and hence, power consuming circumferential slippage between rotor and crop material. Overall, there are very high friction losses, specific power consumption is high and handling of some types of material is unreliable. For example, in damp conditions, there may be a tendency to "roping" of the material leading to plugging of the separator.
Nusser (U.S. Pat. No. 4,178,942) has suggested an axial flow rotary separator which substitutes more or less randomly oscillating tines for the fixed crop engaging elements of conventional rotors and relies entirely on helical guide vanes for axial propulsion. However, the operating characteristics of Nusser's device are not clear from his disclosure.
The intermittently engaging, positively propelling and obliquely moving finger-like crop engaging elements of Witzel's rotor (U.S. Pat. No. 4,408,618) make guide vanes unnecessary and dramatically cut specific power requirement while improving material-handling characteristics and maintaining an acceptable level of separating efficiency. There is no doubt that Witzel's separator represents an important advance over known axial flow rotary separators. However, the embodiments disclosed by Witzel are all relatively complex and the potential total cost of using them, resulting from the related costs of manufacturing and reliability, may make them unattractive.